Cycles Convolution Matrix (Kernel)
The 1st set of nodes (add and subtract nodes) are used  for offset the coordinate .. it is 3*3 convolution filter ..so it can use 9 voronoi/image texture ..so if you adds 0.5 in one of the add node , 1 texture will offset  0.5 unit scale..
If you add/subtract 0 in those node that means that node will not offset .there are 2 add node because 1 is x axis and other one is y axis.
So if you mute those 2 add node it doesn't matter cuz it is not offseting anyway...soorry for my bad English